Beijing residents awakened Monday to skies the eerie yellow color of a
street lamp. It was the second time in three days that the Chinese
capital had been scoured by sandstorms that have hit 16
provinces across west, central and north China, affecting nearly
one-fifth of the country's 1.3 billion people, according to the
state-run Xinhua News Service.

Tiananmen Square was filled with choking whirlwinds, cars and bicycles
were coated in a thin layer of wheat-colored dust, flights were
delayed and on March 20 the air pollution index reached 500  the worst
level possible  due to the high level of particulates in the air. A
day later, several cities in eastern China including Shanghai, Nanjing,
Suzhou and Hangzhou reported similarly bad air quality. Hong Kong and
Taiwan also reported dangerously high levels of pollution. (See pictures of the Mongolian Cyclone dusting up Beijing.)

"What has lead to the floating dust in Beijing is what we call a
'Mongolian cyclone,' a whirlwind caused by low atmospheric pressure,"
says Zhang Mingying, a senior engineer at the Beijing Meteorology
Bureau. "The center of the Mongolian cyclone is usually 800 to 1,000
kilometers to the northwest of Beijing, a vast desert region covering
southern Mongolia and northwestern Inner Mongolia. The cyclone draws
sand and dust particles into high altitudes and together with a strong
north wind, it brings sand grains to nearby areas, and smaller dust
particles further south." (See pictures of China's dust bowl.)

Springtime sandstorms are common in China, as Siberian winds blow dust
and sand off the Gobi desert across east Asia  sometimes as far as North
America. But the size of the storm that began Saturday has surpassed
what China's capital has seen recently. The storms began in desert
areas of the Chinese region of Inner Mongolia and the adjacent central
Asian nation of Mongolia, which is suffering from the combination of a
dry summer followed by a brutally cold winter. The UN has set aside
$3.7 million in aid to help Mongolia recover from the extreme
conditions, which have left thousands short of food and fuel and
killed more than 2 million sheep and other livestock.

In China, the annual sandstorms have been exacerbated by desertification.
Agricultural expansion, overgrazing and population growth starting in
the 1950s strained already dry regions in western China. By 2004, 27%
of the country's landmass suffered from some degree of
desertification, according to the Chinese Meteorological
Administration. China has invested heavily in planting trees and small
shrubs over former croplands to prevent the spread of arid land
eastward. The government has reported the rate of desertification has
slowed after 2000, but says climate change and other environmental
pressures means more than 186,000 square miles (300,000 sq km) of land are still at risk. (Watch a video about desertification in Inner Mongolia.)

While northern China has been battered by sandstorms this spring,
traditionally soggier south China has been battling drought. Premier Wen Jiabao spent the weekend touring drough-stricken villages in Yunnan province, where many areas have received half the usual rainfall. Sixteen
million people in the region are now suffering drinking water
shortages, according to state media. The Dai ethnic group, which is
concentrated near the Burmese border in western Yunnan, has even been
encouraged to cut back on the amount of water used during the upcoming Water
Splashing Festival it celebrates each year to mark the arrival of
spring.